Method and apparatus for producing AlN whiskers, AlN whisker bodies, AlN whiskers, resin molded body, and method for producing resin molded body

ABSTRACT

A method and apparatus for producing AlN whiskers includes reduced incorporation of metal particles, an AlN whisker body, AlN whiskers, a resin molded body, and a method for producing the resin molded body. The method for producing AlN whiskers includes heating an Al-containing material in a material accommodation unit to thereby generate Al gas; and introducing the Al gas into a reaction chamber through a communication portion while introducing nitrogen gas into the reaction chamber through a gas inlet port, to thereby grow AlN whiskers on the surface of an Al2O3 substrate placed in the reaction chamber.

TECHNICAL FIELD

The technique disclosed in the present specification relates to a methodand apparatus for producing AlN whiskers; as well as to an AlN whiskerbody; AlN whiskers; a resin molded body; and a method for producing theresin molded body.

BACKGROUND ART

In general, an electronic device generates heat during use. Thegenerated heat may adversely affect the performance of the electronicdevice. Thus, the electronic device often includes a heat radiationmember. Since the heat radiation member may be required to haveinsulation property, the electronic device may include an insulatingsubstrate.

For example, an AlN substrate may be used as an insulating substrate.Although AlN has both high thermal conductivity and high insulationproperty, the toughness of an AlN substrate is insufficient for someapplications. It is very rare for a material having both high thermalconductivity and high insulation property to be used in applicationsrequiring sufficient brittle fracture strength.

Thus, some of the present inventors have researched and developed amethod for producing AlN whiskers (Patent Document 1). AlN whiskers area fibrous material, and have both high thermal conductivity and highinsulation property. A composite material having various performancescan be produced through solidification of a mixture of AlN whiskers anda resin material.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Patent Application Laid-Open (kokai) No.2014-073951

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

As described above, AlN whiskers are an insulating material. Theconventional production method may cause a problem in that metalparticles (e.g., Al particles) are incorporated into AlN whisker bundlesduring recovery of AlN whiskers. Incorporation of such impurities mayimpair the insulation property of AlN whiskers. Also, incorporation ofimpurities having different atomic radii into AlN crystals may causecrystal defects, resulting in a reduction in thermal conductivity.

The technique disclosed in the present specification has beenaccomplished for solving problems involved in the aforementionedconventional technique. Thus, objects of the technique disclosed in thepresent specification are to provide a method and apparatus forproducing AlN whiskers with reduced incorporation of metal particles; anAlN whisker body; AlN whiskers; a resin molded body; and a method forproducing the resin molded body.

Means for Solving the Problem

In a first aspect, there provided a method for producing AlN whiskers,comprising heating an Al-containing material in a first chamber tothereby generate Al gas; and introducing the Al gas into a secondchamber through a first inlet port while introducing nitrogen gas intothe second chamber through a second inlet port, to thereby grow AlNwhiskers on the surface of an insulating substrate placed in the secondchamber.

In the method for producing AlN whiskers, the first chamber forgenerating Al gas is provided separately from the second chamber forgrowing AlN whiskers, and AlN whiskers are grown on the insulatingsubstrate placed in the second chamber. Thus, incorporation of othermetal particles into the drown AlN whiskers is prevented during recoveryof the AlN whiskers.

Advantageous Effects of the Invention

In the present specification, there are provided a method and apparatusfor producing AlN whiskers with reduced incorporation of metalparticles; an AlN whisker body; AlN whiskers; a resin molded body; and amethod for producing the resin molded body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A partial cross-sectional view of the structure of an AlN whiskeraccording to a first embodiment.

FIG. 2 A schematic illustration of the structure of an apparatus forproducing AlN whiskers according to the first embodiment.

FIG. 3 A partial cross-sectional view of the structure of an AlN whiskerbody according to a second embodiment.

FIG. 4 An explanatory view showing a method for producing AlN whiskerbodies according to the second embodiment (part 1).

FIG. 5 An explanatory view showing the method for producing AlN whiskerbodies according to the second embodiment (part 2).

FIG. 6 A partial cross-sectional view of the structure an AlN whiskeraccording to a third embodiment.

FIG. 7 A schematic illustration of the internal structure of the AlNwhisker according to the third embodiment.

FIG. 8 A cross-sectional view of the structure of a resin molded bodyaccording to a fourth embodiment.

FIG. 9 A schematic illustration of the structure of an apparatus foraligning AlN whiskers according to the fourth embodiment.

FIG. 10 An explanatory view showing a method for producing the resinmolded body according to the fourth embodiment (part 1).

FIG. 11 An explanatory view showing the method for producing the resinmolded body according to the fourth embodiment (part 2).

FIG. 12 An explanatory view showing the method for producing the resinmolded body according to the fourth embodiment (part 3).

FIG. 13 An illustration of the internal structure of a resin molded bodyaccording to a fifth embodiment.

FIG. 14 An illustration of the structure of a thermally conductiveparticulate forming the resin molded body according to the fifthembodiment.

FIG. 15 A schematic illustration of the structure of an apparatus forproducing thermally conductive particulates according to the fifthembodiment.

FIG. 16 A schematic illustration of the structure of a ZrO₂ sensoraccording to a sixth embodiment.

FIG. 17 A perspective view of the external appearance of a catalyticconverter according to a seventh embodiment.

FIG. 18 An enlarged view of the surface of the catalytic converteraccording to the seventh embodiment.

FIG. 19 An enlarged view of the wall of the catalytic converteraccording to the seventh embodiment.

FIG. 20 A perspective view of the external appearance of an automotivewindowpane according to an eighth embodiment.

FIG. 21 An illustration of the internal structure of the automotivewindowpane according to the eighth embodiment.

FIG. 22 A photograph of AlN whiskers grown on an alumina substrate.

FIG. 23 A scanning micrograph of an AlN whisker (AlN whisker body) grownon AlN particles (part 1).

FIG. 24 A scanning micrograph of an AlN whisker (AlN whisker body) grownon AlN particles (part 2).

FIG. 25 A scanning micrograph of AlN whiskers (AlN whisker body) grownon alumina particles (part 1).

FIG. 26 A scanning micrograph of an AlN whisker (AlN whisker body) grownon alumina particles (part 2).

FIG. 27 A cross-sectional view of the structure of a carbon substratecovered with AlN polycrystals.

FIG. 28 A cross-sectional view of the structure of a carbon substratecovered with AlN particles.

FIG. 29 A scanning micrograph of AlN whiskers before hydrophobizationtreatment.

FIG. 30 An oxygen mapping image of an AlN whisker beforehydrophobization treatment as obtained by electron energy lossspectroscopy (part 1).

FIG. 31 An oxygen mapping image of an AlN whisker beforehydrophobization treatment as obtained by electron energy lossspectroscopy (part 2).

FIG. 32 A scanning micrograph of AlN whiskers before hydrophobizationtreatment.

FIG. 33 A scanning micrograph of AlN whiskers after hydrophobizationtreatment.

FIG. 34 A scanning micrograph of the external appearance of AlNwhiskers.

FIG. 35 An enlarged scanning micrograph of an AlN whisker.

FIG. 36 A transmission micrograph of an AlN whisker.

FIG. 37 An image of oxygen atom mapping in an AlN whisker.

MODES FOR CARRYING OUT THE INVENTION

Specific embodiments will next be described with reference to thedrawings by taking, as examples, a method and apparatus for producingAlN whiskers, an AlN whisker body, AlN whiskers, a resin molded body,and a method for producing the resin molded body. The thicknessproportion of each layer shown in the drawings does not correspond toits actual value.

First Embodiment

A first embodiment will now be described.

1. AlN Whisker 1-1. Structure of AlN Whisker

FIG. 1 is a partial cross-sectional view of the structure of an AlNwhisker 100 of the present embodiment. As shown in FIG. 1, the AlNwhisker 100 is a fibrous material. The AlN whisker 100 includes an AlNsingle crystal 110 and an oxygen atom-containing layer 120. The AlNsingle crystal 110 is in a fibrous form. The AlN single crystal 110 islocated at the center of the AlN whisker 100. The AlN whisker 100 has alength of 1 μm to 5 cm. The AlN whisker 100 has a diameter of 0.1 μm to50 μm. These numerical ranges are for reference only and are notnecessarily limited thereto.

1-2. Oxygen Atom-Containing Layer

The oxygen atom-containing layer 120 is a first layer formed throughincorporation of at least oxygen atoms into the AlN single crystal 110.Thus, needless to say, the oxygen atom-containing layer 120 containsoxygen atoms. The oxygen atom-containing layer 120 cylindrically coversthe surface of the AlN single crystal 110. The oxygen atom-containinglayer 120 has a cylindrical shape. The oxygen atom-containing layer 120has a thickness of 7 nm to 500 nm. As described above, the oxygenatom-containing layer 120 is derived from the AlN single crystal 110.Thus, in the case where the AlN single crystal 110 has a sufficientlydense crystalline structure, the oxygen atom-containing layer 120 has athickness of 7 nm to 10 nm. These numerical ranges are for referenceonly and are not necessarily limited thereto.

The oxygen atom-containing layer 120 is formed through reaction betweenthe surface of the AlN single crystal 110 and oxygen molecules or watermolecules contained in air. Thus, the oxygen atom-containing layer 120is derived from a portion of the AlN single crystal 110. The reactionbetween AlN and oxygen molecules or water molecules may generate atleast one of Al₂O₃, AlON, and Al(OH)₃. Therefore, the oxygenatom-containing layer 120 contains at least one of Al₂O₃, AlON, andAl(OH)₃. Alternatively, the oxygen atom-containing layer 120 may beformed of a composite material containing these compounds. Each ofAl₂O₃, AlON, and Al(OH)₃ contains Al atom and an oxygen atom. The oxygenatom-containing la 120 has insulation property. The oxygenatom-containing layer 120 has a thermal conductivity lower than that ofthe AlN single crystal 110.

1-3. Properties of AlN Whisker of the Present Embodiment

The AlN whisker 100 has both high thermal conductivity and highinsulation property. The AlN whisker 100 also has a sufficient brittlefracture strength. Thus, a composite material having various propertiescan be produced through solidification of a mixture of the AlN whisker100 and a resin material.

As described above, the oxygen atom-containing layer 120 is derived froma portion of the AlN single crystal 110. Thus, the oxygenatom-containing layer 120 has a dense crystalline structure. Once theoxygen atom-containing layer 120 is formed, the oxygen atom-containinglayer 120 prevents intrusion of oxygen molecules and water molecules.Thus, the oxygen atom-containing layer 120 effectively preventsoxidation of the AlN single crystal 110 inside of the layer 120. Sincethe oxygen atom-containing layer 120 has excellent crystallinity asdescribed above, the oxygen atom-containing layer 120 achieves a verysmall thickness; i.e., the oxygen atom-containing layer 120 has athickness as small as, for example, 7 nm to 10 nm. Thus, the AlN singlecrystal 110 accounts for a sufficiently large proportion of the volumeof the AlN whisker 100; i.e., the AlN whisker 100 has very high thermalconductivity.

Such a dense oxygen atom-containing layer is difficult to form by use ofa conventional AlN material. Thus, the conventional AlN material has arelatively thick oxide layer or hydroxide layer. The oxide layer of theAlN material does not have high thermal conductivity. In contrast, theAlN whisker 100 of the present embodiment has thermal conductivitysuperior to that of the conventional AlN material, since the oxygenatom-containing layer 120 has a small thickness.

2. AlN Whisker Production Apparatus 2-1. Structure of AlN WhiskerProduction Apparatus

FIG. 2 is a schematic illustration of the structure of a productionapparatus 1000 for producing AlN whiskers 100 of the present embodiment.The production apparatus 1000 includes a furnace body 1100, a heater1400, a nitrogen gas supply unit 1500, and an argon gas supply unit1600. The furnace body 1100 includes therein a material accommodationunit 1200 and a reaction chamber 1300. The furnace body 1100 is formedof, for example, carbon or quartz.

The material accommodation unit 1200 is a first chamber foraccommodating an Al material and generating Al gas through vaporizationof Al. The material accommodation unit 1200 is formed of, for example,carbon or quartz. The material accommodation unit 1200 has a container1210, one or more communication portions 1220, and a gas inlet port1230. The container 1210 is provided for accommodating an Al material.The container 1210 is formed of, for example, alumina. The gas inletport 1230 is provided for introducing a rare gas (e.g., argon gas) intothe material accommodation unit 1200.

The communication portions 1220 communicate between the materialaccommodation unit 1200 and the reaction chamber 1300; i.e., thecommunication portions 1220 are disposed between the materialaccommodation unit 1200 and the reaction chamber 1300. Each of thecommunication portions 1220 has an opening 1220 a facing the materialaccommodation unit 1200 and an opening 1220 b facing the reactionchamber 1300. The opening 1220 b of the communication portion 1220 is afirst inlet port for supplying Al gas generated in the materialaccommodation unit 1200 to the reaction chamber 1300.

The reaction chamber 1300 is a second chamber for reacting Al gas withnitrogen gas to thereby grow AlN whiskers 100. The reaction chamber 1300has Al₂O₃ substrates 1310, gas inlet ports 1320 and 1330, and a gasoutlet port 1340. The Al₂O₃ substrates 1310 are alumina substrates. TheAl₂O₃ substrates 1310 are a type of insulating substrate. The reactionchamber 1300 includes therein a large number of arranged Al₂O₃substrates 1310. Each of the Al₂O₃ substrates 1310 is provided forgrowing AlN whiskers 100 on its surface. The Al₂O₃ substrates 1310 arearranged such that the surfaces of the substrates are orthogonal to thehorizontal direction. The gas inlet port 1320 is a second inlet port forintroducing nitrogen gas into the reaction chamber 1300. The gas inletport 1330 is provided for introducing argon gas into the reactionchamber 1300. The gas outlet port 1340 is provided for discharging gasesfrom the reaction chamber 1300 to the outside of the productionapparatus 1000.

The heater 1400 is provided for heating the interior of the furnace body1100. The heater 1400 is a first heating unit for heating the materialaccommodation unit 1200. Thus, the heater 1400 is used for heating andvaporizing the Al material in the material accommodation unit 1200. Theheater 1400 also heats the reaction chamber 1300. The heater 1400increases the temperature in the reaction chamber 1300.

The nitrogen gas supply unit 1500 is provided for supplying nitrogen gasinto the reaction chamber 1300 through the gas inlet port 1320. Theargon gas supply unit 1600 is provided for supplying argon gas into thereaction chamber 1300 through the gas inlet port 1330. The argon gassupply unit 1600 may be used for supplying argon gas to the materialaccommodation unit 1200 through the gas inlet port 1230.

2-2. Effects of AlN Whisker Production Apparatus and ProductionConditions

The reaction chamber 1300 is disposed above the material accommodationunit 1200; i.e., the material accommodation unit 1200 is disposedvertically below the reaction chamber 1300. Thus, Al gas generated inthe material accommodation unit 1200 readily flows from the materialaccommodation unit 1200 toward the reaction chamber 1300 disposed abovethe unit 1200.

Since the heater 1400 simultaneously heats the material accommodationunit 1200 and the reaction chamber 1300, substantially no difference intemperature resides between the material accommodation unit 1200 and thereaction chamber 1300. The growth temperature of AlN whiskers 100 is1,500° C. to 1,800° C. The substrate temperature is almost the same asthe temperature of the atmosphere in the furnace. The internal pressuresof the material accommodation unit 1200 and the reaction chamber 1300are almost equal to atmospheric pressure. Preferably, the internalpressure of the material accommodation unit 1200 is slightly higher thanthat of the reaction chamber 1300. In such a case, nitrogen gas in thereaction chamber 1300 barely enters the material accommodation unit1200. Thus, the surface of the molten Al material is barely nitrided.

3. Production Method for AlN Whiskers 3-1. Material Provision Step

Firstly, an Al material is accommodated in the container 1210 of theproduction apparatus 1000. The Al material is industrially smeltedaluminum. In this step, the Al material is in the form of solid metal.

3-2. Vaporization Step (Al Gas Generation Step)

Subsequently, the Al material is heated in the material accommodationunit 1200, to thereby generate Al gas. For this purpose, the furnacebody 1100 is heated by means of the heater 1400. This heating increasesthe temperatures in the material accommodation unit 1200 and thereaction chamber 1300. During heating of the material accommodation unit1200, the argon gas supply unit 1600 supplies argon gas into thematerial accommodation unit 1200. When the temperature reaches themelting point of Al, the Al material starts to melt. Thereafter, aportion of the Al material starts to vaporize even at a temperaturebelow the boiling point of Al; i.e., the Al material vaporizes togenerate Al gas. Thus, the interior of the material accommodation unit1200 is filled with a gas mixture of argon gas and Al gas.

3-3. AlN Single Crystal Formation Step (Gas Supply Step)

Subsequently, the gas mixture of argon gas and Al gas is caused to flowfrom the material accommodation unit 1200 into the reaction chamber 1300through the openings 1220 b of the communication portions 1220. In thiscase, the gas mixture of Al gas and argon gas is supplied into thereaction chamber 1300 in a direction almost parallel to the surfaces ofthe Al₂O₃ substrates 1310. Meanwhile, the argon gas supply unit 1600supplies argon gas into the reaction chamber 1300 through the gas inletport 1330. Preferably, Al gas is supplied to the Al₂O₃ substrates 1310after the space around the Al₂O₃ substrates 1310 has been filled with Argas. The nitrogen gas supply unit 1500 supplies nitrogen gas into thereaction chamber 1300 through the gas inlet port 1320. Then, argon gas,Al gas, and nitrogen gas are mixed together in the reaction chamber1300. Thus, Al gas reacts with nitrogen gas on the surfaces of the Al₂O₃substrates 1310, to thereby grow fibrous AlN single crystals 110.

The growth temperature of the AlN single crystals 110 is 1,500° C. to1,800° C. Thus, the atmosphere temperature in the reaction chamber 1300is adjusted to 1,500° C. to 1,800° C. during growth of the AlN singlecrystals 110. Since the production time for the AlN single crystals 110is sufficiently long, the substrate temperature is probably almost equalto the atmosphere temperature. Thus, the temperature of the Al₂O₃substrates 1310 is 1,500° C. to 1,800° C. The internal pressure of thereaction chamber 1300 is almost 1 atm; i.e., the internal pressure fallswithin a range of 0.9 atm to 1.1 atm.

3-4. Oxygen Atom-Containing Layer Formation Step

Thereafter, the furnace temperature of the production apparatus 1000 islowered to room temperature. The AlN single crystals 110 are thenremoved from the production apparatus 1000. During removal of the AlNsingle crystals 110 or temperature drop, the surfaces of the AlN singlecrystals 110 probably react with oxygen molecules or water molecules, tothereby form oxygen atom-containing lavers 120. Thus, thin oxygenatom-containing layers 120 are formed on the surfaces of the AlN singlecrystals 110 removed from the production apparatus 1000.

4. Effects of the Present Embodiment 4-1. Purity of AlN Whiskers

The technique of the present embodiment does not involve the use of Tior Si as a growth activator unlike the technique disclosed in JapanesePatent Application Laid-Open (kokai) No. 2014-073951. Since a metalcatalyst is not used the present embodiment, metal aggregates are barelyformed around AlN whiskers 100. Since the Al material used as a rawmaterial has high-purity Al, virtually no impurities enter the AlNwhiskers 100. Thus, the thus-produced AlN whiskers 100 have high purity.In the present embodiment, Al₂O₃ probably plays a catalyst-like role.

4-2. AlN Powder and Yield

Virtually no AlN powder enters the AlN whiskers 100. Thus, the yield ofthe AlN whiskers 100 relative to the raw material is very high.

4-3. Productivity of AlN Whiskers

In the present embodiment, the material accommodation unit 1200 isdisposed separately from the reaction chamber 1300; i.e., Al gas and AlNare generated at different sites. In addition, the internal pressure ofthe material accommodation unit 1200 is higher than that of the reactionchamber 1300. Therefore, nitrogen gas barely enters the materialaccommodation unit 1200; hence, the surface of the molten Al material isbarely nitrided. Thus, the Al material can be supplied to the reactionchamber 1300 over a long period of time. Consequently, long AlN whiskers100 can be produced in the present embodiment.

In the conventional technique (see, for example, Japanese PatentApplication Laid-Open (kokai) No. 2014-073951), AlN whiskers aregenerated at the surface of a molten material containing Al—Ti—Si as amain component; i.e., the growth site of AlN whiskers is limited to thesurface of the molten material. Thus, the conventional techniquerequires a very large furnace for mass production of AlN whiskers.

In the present embodiment, AlN whiskers 100 are grown through reactionbetween Al gas and nitrogen gas on the surfaces of the Al₂O₃ substrates1310. Thus, the growth site of AlN whiskers 100 is not necessarilylimited to the surface (horizontal surface) of the molten material.Therefore, a large amount of AlN whiskers 100 can be produced on thesurfaces or a large number of Al₂O₃ substrates 1310 disposed orthogonalto the horizontal surface by means of a relatively small furnace.

5. Modifications 5-1. Shutter of Opening

The communication portions 1220 are located between the materialaccommodation unit 1200 and the reaction chamber 1300. The opening 1220a or 1220 b of each communication portion 1220 may be provided with anopenable and closable shutter. The shutter is a unit for switching theopen state and the closed state of the opening 1220 a or 1220 b. Theshutter can control the timing of flow of Al gas into the reactionchamber 1300.

5-2. Heating Unit

As shown in FIG. 2, the material accommodation unit 1200 is disposed inthe interior of the furnace body 1100. However, the materialaccommodation unit 1200 and the reaction chamber 1300 may be provided asindependent units. In such a case, the production apparatus 1000includes a first heating unit for heating the material accommodationunit 1200 and a second heating unit for heating the reaction chamber1300. Thus, the material accommodation unit 1200 and the reactionchamber 1300 can be separately heated. Therefore, the temperature forvaporizing the Al material can be adjusted separately from the furnacetemperature of the reaction chamber 1300.

5-3. Insulating Substrate

The Al₂O₃ substrate 1310 used in the present embodiment is an aluminasubstrate. The Al₂O₃ substrate 1310 may be a sapphire substrate. Thus,examples of the Al₂O₃ substrate include an alumina substrate and asapphire substrate. The insulating substrate may be an AlNpolycrystalline substrate.

5-4. Al-Containing Material

The Al material used in the present embodiment is industrially refinedaluminum. However, an Al alloy may be used instead of such a high-purityAl material. AlN whiskers 100 can be produced even if such an Alatom-containing material is used. However, the use of industriallyrefined aluminum can reduce incorporation of impurities into theproduced AlN whiskers 100.

5-5. Combination

The aforementioned modifications may be combined in any manner.

6. Summary of the Present Embodiment

In the production method for the AlN whiskers 100 of the presentembodiment, Al gas is generated in the material accommodation unit 1200,and Al gas is mixed with nitrogen gas in the reaction chamber 1300, tothereby-grow the AlN whiskers 100 on the surfaces of the Al₂O₃substrates 1310. Thus, the AlN whiskers 100 are produced.

The AlN whiskers 100 of the present embodiment have a very high purity.Since Ti or Si is not used as a catalyst, the AlN whiskers 100 containvirtually no impurities. Virtually no AlN powder is generated during theproduction process.

Second Embodiment

A second embodiment will now be described.

1. AlN Whisker Body

FIG. 3 is a partial cross-sectional view of the structure of an AlNwhisker body 200 of the present embodiment. The AlN whisker body 200includes an AlN whisker 100 and an AlN particle 210. The AlN whisker 100is bonded to the surface 211 of the AlN particle 210. Thus, in the AlNwhisker body 200, the AlN whisker 100 is integrated with the AlNparticle 210. The AlN particle 210 has a size of about 0.2 μm to about10 mm.

2. Production Method for AlN Whisker Body

The production method for the AlN whisker body 200 is almost the same asthe production method for the AlN whiskers 100 of the first embodiment.Thus, differences between these methods will now be described.

2-1. AlN Particle Provision Step

FIG. 4 shows an AlN particle accommodation unit B1 accommodating AlNparticles 210. In the present embodiment, the AlN particles 210 areaccommodated in the AlN particle accommodation unit B1 as shown in FIG.4. The reaction chamber 1300 includes therein the AlN particleaccommodation unit B1 instead of the Al₂O₃ substrates 1310. Thus, theAlN particles 210 are used as insulating substrates in the presentembodiment.

2-2. Material Provision Step

An Al material is accommodated in the container 1210 of the productionapparatus 1000.

2-3. Vaporization Step (Al Gas Generation Step)

This step is performed in the same manner as the vaporization step ofthe first embodiment.

2-4. AlN Single Crystal Formation Step (Gas Supply Step)

This step is performed in the same manner as the AlN single crystalformation step of the first embodiment.

2-5. Oxygen Atom-Containing Layer Formation Step

This step is performed in the same manner as the oxygen atom-containinglayer formation step of the first embodiment. Thus, as shown in FIG. 5,AlN whiskers 100 are grown on the surfaces 211 of the AlN particles 210.

3. Effects of the Present Embodiment

The AlN whisker body 200 of the present embodiment includes the AlNwhisker 100 and the AlN particle 210. The AlN whisker body 200 has thecenter of gravity in the vicinity of the AlN particle 210. Thus, a resincontaining the AlN whisker body 200 is readily formed into a flat moldedbodiesuch that the AlN particle 210 side of the AlN whisker body 200 islocated at a first surface (front surface) and the AlN whisker 100 sideof the AlN whisker body 200 is located at a second surface (backsurface). This process can produce a resin molded body wherein a thermalconduction path extends between the front surface and the back surface.

4. Modifications 4-1. Insulating Substrate

The insulating substrate may be Al₂O₃ particles instead of AlNparticles. As described in the first embodiment and its modifications,the insulating substrate may be any of an Al₂O₃ substrate, an AlNpolycrystalline substrate, AlN particles, and Al₂O₃ particles. Thus, theinsulating substrate may be composed of an Al atom-containing material.

4-2. Insulating Substrate Covering Carbon Substrate

The insulating substrate may cover a carbon substrate. For example, atleast one of AlN polycrystals and AlN particles may be formed on thecarbon substrate. In such a case, the AlN whisker body includes thecarbon substrate, the AlN polycrystal or AlN particle formed on thesurface of the carbon substrate, and an AlN whisker bonded to thesurface of the AlN polycrystal or the AlN.

The AlN polycrystal or AlN particle on the carbon substrate can beformed by means of vapor deposition, sputtering, or MOCVD. When the AlNwhisker production process is repeated while the carbon substrate isplaced in the production apparatus 1000, AlN polycrystals or AlNparticles are formed on the carbon substrate. Thus, the insulatingsubstrate covering the carbon substrate may be synthesized during theAlN whisker production process.

The carbon substrate has excellent thermal resistance. The surface ofthe carbon substrate is thoroughly covered with AlN polycrystals or AlNparticles. AlC is probably formed at the interface between the carbonsubstrate and the AlN polycrystals or the AlN particles. Thus, strongbonding is achieved between the carbon substrate and the AlNpolycrystals or the AlN particles. Therefore, incorporation of carboninto AlN whiskers can be prevented during recovery of the AlN whiskers.

4-3. Combination

The aforementioned modifications may be combined in any manner.

Third Embodiment

A third embodiment will now be described.

1. AlN Whisker 1-1. Structure of AlN Whisker

FIG. 6 is a partial cross-sectional view of the structure of an AlNwhisker 300 of the present embodiment. As shown in FIG. 6, the AlNwhisker 300 is a fibrous material. The AlN whisker 300 includes an AlNsingle crystal 310, an oxygen atom-containing layer 320, and ahydrophobic layer 330. The AlN single crystal 310 is in a fibrous form.The AlN whisker 300 has a length of 1 μm to 5 cm. The AlN whisker 300has a diameter of 0.1 μm to 50 μm. These numerical ranges are forreference only and are not necessarily limited thereto.

1-2. Oxygen Atom-Containing Layer

The oxygen atom-containing layer 320 is a first layer formed throughincorporation of at least oxygen atoms into the AlN single crystal 310.The oxygen atom-containing layer 320 cylindrically covers the surface ofthe AlN single crystal 310. The oxygen atom-containing layer 320 has acylindrical shape. The oxygen atom-containing layer 320 has a thicknessof 7 nm to 500 nm. As described above, the oxygen atom-containing layer320 is derived from the AlN single crystal 310. Thus, when the AlNsingle crystal 310 has a sufficiently dense crystalline structure, theoxygen atom-containing layer 320 has a thickness of 7 nm to 10 nm. Thesenumerical ranges are for reference only and are not necessarily limitedthereto.

The oxygen atom-containing layer 320 is formed through reaction betweenthe surface of the AlN single crystal 310 and oxygen molecules or watermolecules contained in air. Thus, the oxygen atom-containing layer 320is derived from a portion of the AlN single crystal 310. The reactionbetween AlN and oxygen molecules or water molecules may generate atleast one of Al₂O₃, AlON, and Al(OH)₃. Therefore, the oxygenatom-containing layer 320 contains at least one of Al₂O₃, AlON, andAl(OH)₃. Alternatively, the oxygen atom-containing layer 320 may beformed of a composite material containing these compounds. Each ofAl₂O₃, AlON, and Al (OH)₃ contains an Al atom and an oxygen atom. Theoxygen atom-containing layer 320 has insulation property. The oxygenatom-containing layer 320 has a thermal conductivity lower than that ofthe AlN single crystal 310.

1-3. Hydrophobic Layer

The hydrophobic layer 330 is a second layer exhibiting hydrophobicity.The hydrophobic layer 330 is the outermost layer of the AlN whisker 300.The hydrophobic layer 330 cylindrically covers the surface of the oxygenatom-containing layer 320. The hydrophobic layer 330 has a cylindricalshape. The hydrophobic layer 330 has a thickness of, for example, 1 nmto 50 nm.

The hydrophobic layer 330 has hydrocarbon groups. Al atoms of the oxygenatom-containing layer 320 are bonded via an ester bond to hydrocarbongroups of the hydrophobic layer 330. The hydrophobic layer 330 is formedthrough bonding of a fatty acid to at least one of Al₂O₃, AlON, andAl(OH)₃ contained in the oxygen atom-containing layer 320. Examples ofthe fatty acid include a saturated fatty acid and an unsaturated fattyacid. Examples of the saturated fatty acid include stearic acid. Thus,the “hydrocarbon group” as used herein consists of a carbon atom(s) anda hydrogen atom(s). The hydrocarbon group contains any number of carbonatoms. The hydrophobic layer 330 has insulating property. Thehydrophobic layer 330 has a thermal conductivity lower than that of theAlN single crystal 310.

FIG. 7 is a schematic illustration of the internal structure of the AlNwhisker 300 of the present embodiment. As shown in FIG. 7, the oxygenatom-containing layer 320 is disposed outside of the AlN single crystal310, and the hydrophobic layer 330 is disposed outside of the oxygenatom-containing layer 320 and has hydrocarbon groups bonded via an esterbond to the oxygen atom-containing layer 320. The oxygen atom-containinglayer 320 bonded via an ester bond to the hydrophobic layer 330 containsany of Al₂O₃, AlON, and Al(OH)₃.

1-4. Properties of AlN Whisker of the Present Embodiment

The AlN whisker 300 has both high thermal conductivity and highinsulation property. The AlN whisker 300 also has sufficient brittlefracture strength. The hydrophobic layer 330 is readily bonded to aresin material; i.e., the hydrophobic layer 330 achieves sufficientlyhigh adhesion to a resin material. Thus, when the AlN whisker 300 ismixed with a resin material and the mixture is solidified, the resultantcomposite material can achieve high adhesion between the AlN whisker 300and the resin material.

As described above, the oxygen atom-containing layer 320 is derived froma portion of the AlN single crystal 310. Thus, the oxygenatom-containing layer 320 has a dense crystalline structure. Once theoxygen atom-containing layer 320 is formed, the oxygen atom-containinglayer 320 prevents intrusion of oxygen molecules and water molecules.Thus, the oxygen atom-containing layer 320 has a thickness as small as,for example, 7 nm to 10 nm. Therefore, the AlN single crystal 310accounts for a sufficiently large proportion of the volume of the AlNwhisker 300; i.e., the AlN whisker 300 has very high thermalconductivity.

Such a dense oxygen atom-containing layer is difficult to form in aconventional AlN material. Thus, the conventional AlN material includesa relatively thick oxide layer (or hydroxide layer) Since the oxygenatom-containing layer 320 having low thermal conductivity has a smallthickness in the present embodiment, the AlN whisker 300 of the presentembodiment has thermal conductivity superior to that of the conventionalAlN material.

2. Production Method for AlN Whiskers 2-1. Material Provision Step

This step is performed in the same manner as the material provision stepof the first embodiment.

2-2. Vaporization Step (Al Gas Generation Step)

This step is performed in the same manner as the vaporization step ofthe first embodiment.

2-3. AlN Single Crystal Formation Step (Gas Supply Step)

This step is performed in the same manner as the AlN single crystalformation step of the first embodiment.

2-4. Oxygen Atom-Containing Layer Formation Step

This step is performed in the same manner as the oxygen atom-containinglayer formation step of the first embodiment.

2-5. Hydrophobic Layer Formation Step (Surface Treatment Step)

Subsequently, the hydrophobic layer 330 (hydrocarbon groups) is formedon the surface of the oxygen atom-containing layer 320. For formation ofthe hydrocarbon groups, the AlN single crystal 310 having the oxygenatom-containing layer 320 is mixed with stearic acid and cyclohexane.The resultant mixture is heated to the boiling point of the solvent andthen refluxed. Subsequently, the mixture is cooled to 40° C. and thensubjected to filtration. Thereafter, the resultant product is washedwith cyclohexane, followed by drying under reduced pressure, to therebyform the hydrophobic layer 330 on the surface of the oxygenatom-containing layer 320.

3. Effects of the Present Embodiment 3-1. Effects of Hydrophobic Layer

The AlN whisker 300 of the present embodiment includes the hydrophobiclayer 330 disposed outside of the oxygen atom-containing layer 320. Thehydrophobic layer 330 is formed through hydrophobization treatment ofthe surface of the oxygen atom-containing layer 320. The hydrophobiclayer 330 readily adheres to a resin material. Thus, when the AlNwhisker 300 of the present embodiment is mixed with a resin material andthe mixture is solidified, virtually no gaps are generated around theAlN whisker 300.

3-2. Purity of AlN Whiskers

The technique of the present embodiment does not involve the use of Tior Si as a growth activator unlike the technique disclosed in JapanesePatent Application Laid-Open (kokai) No. 2014-073951. Since a metalcatalyst is not used in the present embodiment, metal aggregates arebarely formed around AlN whiskers 300. Since the Al material used as araw material has high-purity Al, virtually no impurities enter the AlNwhiskers 300. Thus, the thus-produced AlN whiskers 300 have high purity.In the present embodiment, Al₂O₃ probably plays a catalyst-like role.

3-3. AlN Powder and Yield

Virtually no AlN powder enters the AlN whiskers 300. Thus, the yield ofthe AlN whiskers 300 relative to the raw material is very high.

3-4. Productivity of AlN Whiskers

In the present embodiment, the material accommodation unit 1200 isdisposed separately from the reaction chamber 1300; i.e., Al gas and AlNare generated at different sites. In addition, the internal pressure ofthe material accommodation unit 1200 is higher than that of the reactionchamber 1300. Therefore, nitrogen gas barely enters the materialaccommodation unit 1200; hence, the surface of the molten Al material isbarely nitrided. Thus, the Al material can be supplied to the reactionchamber 1300 over a long period of time. Consequently, long AlN whiskers300 can be produced in the present embodiment.

In the conventional technique (see, for example, Japanese PatentApplication Laid-Open (kokai) No. 2014-073951), AlN whiskers aregenerated at the surface of a molten material containing Al—Ti—Si as amain component; i.e., the growth site of AlN whiskers is limited to thesurface of the molten material. Thus, the conventional techniquerequires a very large furnace for mass production of AlN whiskers.

In the present embodiment, AlN whiskers are grown through reactionbetween Al gas and nitrogen gas on the surfaces of the Al₂O₃ substrates1310. Thus, the growth site of AlN whiskers is not necessarily limitedto the surface (horizontal surface) of the molten material. Therefore, alarge amount of AlN whiskers can be produced on the surfaces of a largenumber of Al₂O₃ substrates 1310 by means of a relatively small furnace.

4. Modifications 4-1. Oxygen Atom-Containing Layer

The oxygen atom-containing layer 320 contains at east one of Al₂O₃,AlON, and Al(OH)₃. However, the oxygen atom-containing layer 320 maycontain an oxygen atom-containing Al compound other than theaforementioned Al compounds. Thus, the oxygen atom-containing layer 320is a layer containing an Al atom and an oxygen atom.

5. Summary of the Present Embodiment

The AlN whisker 300 of the present embodiment includes the AlN singlecrystal 310, the oxygen atom-containing layer 320, and the hydrophobiclayer 330. Since the hydrophobic layer 330 has hydrocarbon groups, theAlN whisker 300 has high adhesion to a resin material. Thus, a mixtureof the AlN whisker 300 of the present embodiment and a resin materialcan be formed into a composite material having excellent thermalconductivity.

Fourth Embodiment

A fourth embodiment will now be described. The fourth embodimentcorresponds to a resin molded body produced through molding of a resinin which fibrous AlN whiskers are aligned in one direction, and a methodfor producing the resin molded body.

1. Resin Molded Body

FIG. 8 shows the internal structure of a resin molded body 400 of thepresent embodiment. The resin molded body 400 contains AlN whiskers 300of the third embodiment and a resin 410. Each of the AlN whiskers 300has a first end 300 a and a second end 300 b. The resin 410 is a resinmaterial covering the AlN whiskers 300. Thus, gaps between the AlNwhiskers 300 are filled with the resin 410. The resin molded body 400has a first surface 400 a and a second surface 400 b. The second surface400 b is opposite the first surface 400 a.

As shown in FIG. 8, the AlN whiskers 300 extend between the firstsurface 400 a and the second surface 400 b in the resin molded body 400.That is, the first ends 300 a of the AlN whiskers 300 are exposed at thefirst surface 400 a, and the second ends 300 b of the AlN whiskers 300are exposed at the second surface 400 b. Thus, the AlN whiskers 300penetrate through the resin molded body 400 between the first surface400 a and the second surface 400 b.

The AlN whiskers 300 form thermal conduction paths between the firstsurface 400 a and the second surface 400 b. In the resin molded body400, the thermal conduction paths are present at high density. Thus,heat is effectively conducted from the first surface 400 a to the secondsurface 400 b. Gaps between the AlN whiskers 300 are filled with theresin 410. Since the resin 410 has a thermal conductivity lower thanAlN, heat is less likely to diffuse in the planar direction of the resinmolded body 400.

The AlN whiskers 300 are not necessarily disposed perpendicular to thesurfaces of the resin molded body 400. As shown in FIG. 8, the angle θbetween the axial direction of the AlN whiskers 300 and the firstsurface 400 a is 60° to 120° in the resin molded body 400. The angle θis preferably 75° to 105°. Needless to say, the angle θ is preferably90°.

FIG. 8 shows a small number of AlN whiskers 300 for the sake of clarity.In actuality, the AlN whiskers 300 are present at much higher density.

2. AlN Whisker Alignment Apparatus

FIG. 9 shows an alignment apparatus 2000 for aligning AlN whiskers 300of the present embodiment. As shown in FIG. 9, the alignment apparatus2000 is used for aligning bundles of AlN whiskers 300 entangled andextending in different directions. The alignment apparatus 2000 has acontainer 2001, a lid 2002, an AlN whisker placement unit 2100, a flowchannel 2110, an air inlet port 2120, electrodes 2200 a and 2200 b, anda tape 2300.

The container 2001 has the IN whisker placement unit 2100, the flowchannel 2110, and the air inlet port 2120. The lid 2002 is provided fortemporarily sealing the container 2001. The electrode 2200 b and thetape 2300 are fixed to the lid 2002.

The AlN whisker placement unit 2100 is provided for placing the AlNwhiskers 300 in the initial state. The AlN whiskers 300 in the initialstate are entangled and extend in different directions. The AlN whiskerplacement unit 2100 has through holes 2100 a. The through holes 2100 aare provided for ejecting air flowing through the flow channel 2110 fromthe AlN whisker placement unit 2100 toward the lid 2002.

The flow channel 2110 is located vertically below the AlN whiskerplacement unit 2100 and is provided for causing air to flowtherethrough. The air inlet port 2120 is provided for introducing airinto the flow channel 2110.

The electrodes 2200 a and 2200 b are disposed such that the AlN whiskerplacement unit 2100 is located therebetween. The electrode 2200 a isdisposed outside and below the container 2001. The AlN whiskers 300 canbe flown from the AlN whisker placement unit 2100 toward the electrode2200 b by application of voltage between the electrodes 2200 a and 2200b.

The tape 2300 is provided for bonding the flown AlN whiskers 300thereto. An adhesive 2400 is applied to the surface of the tape 2300facing the AlN whisker placement unit 2100 for effectively bonding theflown AlN whiskers 300 to the tape 2300.

3. AlN Whisker Alignment Method 3-1. Dispersion Step

Firstly, bundles of AlN whiskers 300 are placed on the AlN whiskerplacement unit 2100 of the alignment apparatus 2000. In this step,numerous AlN whiskers 300 are entangled with one another. Subsequently,air is supplied through the air inlet port 2120, whereby air is ejectedvia the through holes 2100 a toward the lid 2002. Thus, AlN whiskers 300temporarily fly in the air. The bundles of AlN whiskers 300 are loosenedby repetition of air supply and interruption of air supply.

3-2. Voltage Application Step

Subsequently, DC voltage is applied between the electrodes 2200 a and2200 b. This generates an electric field at the AlN whiskers 300, and inthe vicinity thereof. Since the AlN whiskers 300 are electrostaticallycharged, the AlN whiskers 300 fly in the air by means of the electricfield. Then, the first ends 300 a of the AlN whiskers 300 adhere to thetape 2300. Thereafter, application of the voltage between the electrodes2200 a and 2200 b is terminated.

In this step, some of the AlN whiskers 300 adhere to the tape 2300.However, the density of the AlN whiskers 300 adhering to the tape 2300is relatively low. Therefore, application of DC voltage between theelectrodes 2200 a and 2200 b and termination of the voltage applicationare repeated a plurality of times, to thereby increase the density ofthe AlN whiskers 300 adhering to the tape 2300. After the AlN whiskers300 have been bonded to the tape 2300 at high density, the AlN whiskers300 adhering to the tape 2300 are removed from the apparatus.

In some cases, air may be introduced through the air inlet port 2120during application of DC voltage between the electrodes 2200 a and 2200b, so that the AlN whiskers 300 are efficiently bonded to the tape 2300.

4. Resin Molding Method

Subsequently, a resin is molded while the AlN whiskers 300 are alignedupright.

4-1. AlN Whisker Provision Step

As shown in FIG. 10, there are firstly provided the AlN whiskers 300whose first ends 300 a adhere to the tape 2300. As shown in FIG. 10, thetape 2300 is located below the AlN whiskers 300. The tape 2300 may belocated above the Al whiskers 300.

4-2. Resin Impregnation Step

Subsequently, as shown in FIG. 11, a resin added to gaps between the AlNwhiskers 300 aligned upright. Thus, while the first ends 300 a of theAlN whiskers 300 adhere to the tape 2300, the AlN whiskers 300 areimpregnated with a liquid-form resin, whereby the gaps between the AlNwhiskers 300 are filled with the resin. The resin is then solidified.

4-3. Tape Removal Step

Subsequently, as shown in FIG. 12, the tape 2300 is removed from theupright AlN whiskers 300 contained in the solidified resin. That is, thetape 2300 is removed from the first ends 300 a of the AlN whiskers 300.

5. Tape and Resin Materials 5-1. Tape Material

Examples of the material of the tape 2300 include foamed tape,polyolefin tape, acrylic tape, heat-resistant polyimide, heat-resistantinsulating Nomex, glass cloth tape, high-strength and high-insulationPPS base, PP base, polyester tape, and fluororesin tape. Examples of theadhesive 2400 include rubber adhesive, acrylic adhesive, siliconeadhesive, and urethane adhesive.

5-2. Resin Material

Examples of the usable resin include thermosetting reins, such assilicone resin (SI), epoxy resin (EP), phenolic resin (PF), melamineresin (MF), urea resin (UF), thermosetting polyimide (PI), unsaturatedpolyester resin (FRP) glass fiber reinforced plastic (FRP), andpolyurethane (PU).

Other examples of the usable resin include thermoplastic resins, such aspolyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinylchloride (PVC), polyvinylidene chloride (PVDC), polyvinyl acetate(PBAc), acrylonitrile-styrene copolymer (AS),acrylonitrile-butadiene-styrene copolymer (ABS),acrylonitrile-ethylene-propylene-diene-styrene copolymer (AES), andmethacrylic resin (PMMA).

Other examples of the usable resin include fluororesins, such aspolytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE),polyvinylidene fluoride (PVDF), and polyvinyl fluoride (PVF).

Other examples of the usable resin include polycarbonate (PC), polyamideresin (PA), polyacetal (POM), polyethylene terephthalate (PET),polybutylene terephthalate (PET), polyether ether ketone (PEEK),polyphenylene sulfide (PPS), polysulfone (PSF), polyether imide (PEI),polyamide imide (PAI), thermoplastic polyimide (PI), and liquid crystalpolymer (LCP).

Other examples of the resin include acrylonitrile styrene acrylate(ASA), atactic polypropylene (APP), cellulose acetate (CA), celluloseacetate butyrate (CAB), chlorinated vinyl chloride (CPVC), chloroprenerubber (CR), diallyl phthalate (DAP), ethylene ethyl acrylate (EEA),ethylene-propylene-diene terpolymer (EPDM), ethylene-tetrafluoroethylenecopolymer (ETFE), ethylene-vinyl acetate copolymer (EVA), ethyl vinylether (EVE), ethylene-vinyl alcohol copolymer (EVOH), perfluoro rubber,tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and softurethane foam (FPF).

Other examples of the resin include glass fiber reinforced plastic(FRP), glass fiber reinforced thermoplastic plastic (FRTP), butyl rubber(IIR), ionomer (IO), isoprene rubber (IR), melamine formaldehyde (MF),methyl methacrylate (MMA), nitrile rubber (NBR), natural rubber (NR),polyacrylic acid (PAA), polyallyl ether ketone (PAEK), polyester alkydresin (PAK), polyacrylonitrile (PAN), and polyarylate (PAR).

Other examples of the resin include polyparaphenylene benzobisoxazole(PBO), polybutadiene styrene (PBS), polycarbonate (PC), diallylterephthalate (DAP), polvdicyclopentadiene (PDCPD), polyethylenenaphthalate (PEN), polyethylene oxide (PEO), polyether sulfone (PES),phenol formaldehyde (PF), tetrafluoroethylene-perfluoroalkyl vinyl ethercopolymer (PFA), polyisobutylene (PIB), and polymethylpentene (PMP).

Other examples of the resin include polyphthalamide (PPA), polyphenyleneether (PPE), polyphenylene oxide (PPO), polytrimethylene terephthalate(PTT), reactive polyurethane (PUR), polyvinyl alcohol (PVA), polyvinylbutyral (PVB), acrylic-modified polyvinyl chloride, polyvinyl dichloride(PVD), and vinyl chloride-vinyl acetate copolymer (PVCA).

Other examples of the resin include polyvinyl formal (PVF),polyvinylpyrrolidone (PVP), styrene butadiene (SB), styrene-butadienerubber (SBR), styrene block copolymer (SBC), styrene-butadiene-styreneblock copolymer (SBS), styrene-ethylene-butylene-styrene block copolymer(SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS),styrene-isoprene-styrene block copolymer (SIS), sheet molding compound(SMC), syndiotactic polystyrene (SPS), thermoplastic elastomer (TPE),thermoplastic polyurethane (TPU), urea formaldehyde resin (UF),ultra-high molecular weight polyethylene (UHMWPE), vinyl chlorideethylene (VCE), vinyl chloride octyl acrylate (VCOA), and crosslinkedpolyethylene (XLPE).

6. Method for Producing AlN Whisker Resin Molded Body 6-1. AlN WhiskerProduction Step

AlN whiskers 300 are produced as descried in the third embodiment.

6-2. AlN Whisker Alignment Step

As described in the present embodiment, AlN whiskers 300 aligned uprightare bonded to a tape 2300.

6-3. Resin Molding Step

As described in the present embodiment, the aligned AlN whiskers 300 aresolidified with a resin. The tape 2300 is removed from the AlN whiskers300, to thereby produce a resin molded body.

7. Modifications 7-1. AlN Whiskers

The AlN whiskers 300 used in the fourth embodiment are as described inthe third embodiment. However, the AlN whiskers used may be other thanthose described in the third embodiment.

7-2. Pressure Reduction Step

After introduction of the resin into the gaps between the AlN whiskers300, pressure may be reduced while the tape 2300 is bonded to the firstends 300 a of the AlN whiskers 300. Pressure reduction beforesolidification of the resin can remove air present between the AlNwhiskers 300 and the resin. After hardening of the resin, these membersare placed under atmospheric pressure. This step can further improve theadhesion between the AlN whiskers 300 and the resin 410.

7-3. Combination

The aforementioned modifications may be combined in any manner.

Fifth Embodiment

A fifth embodiment will now be described. A resin molded body of thefifth embodiment contains insulating particles and AlN whiskers.

1. Resin Molded Body

FIG. 13 shows the internal structure of a resin molded body 500 of thepresent embodiment. The resin molded body 500 contains AlN whiskers 300of the third embodiment, insulating particles 510, and a resin 520. Theinsulating particles 510 have high insulation property and high thermalconductivity. Examples of the insulating particles 510 include aluminaparticles, AlN particles, and silicon nitride particles. Needless tosay, the insulating particles 510 may be other particles. However, theinsulating particles 510 are preferably formed of a material having highthermal conductivity. A plurality of AlN whiskers 300 cover theinsulating particles 510. The resin 520 covers the AlN whiskers 300. Aportion of the resin 520 may cover a portion of the surfaces of theinsulating particles 510 through gaps between the AlN whiskers 300. Thetype of the resin 520 may be the same as the resin 410 used in thefourth embodiment.

2. Thermally Conductive Particulate

FIG. 14 shows the structure of a thermally conductive particulate TP1,The thermally conductive particulate TP1 contains an insulating particle510 and AlN whiskers 300. The thermally conductive particulate TP1 hashigh thermal conductivity and high insulating property. As shown in FIG.14, the surface of the insulating particle 510 is covered with numerousAlN whiskers 300 in the thermally conductive particulate TP1. Thenumerous AlN whiskers 300 are bonded to the insulating particle 510 bymeans of an adhesive 511.

As shown in FIG. 13, the AlN whiskers 300 of adjacent thermallyconductive particulates TP1 are in contact with one another in the resinmolded body 500. For example, the AlN whiskers 300 of a first thermallyconductive particulate TP1 are in contact with the AlN whiskers 300 of asecond thermally conductive particulate TP1.

3. Thermally Conductive Particulate Production Apparatus

FIG. 15 shows a production apparatus 3000 for producing thermallyconductive particulates TP1. The production apparatus 3000 has acontainer 3100, an air pump 3200, a particle inlet port 3300, and aheater 3400.

The container 3100 accommodates AlN whiskers 300 and also serves as achamber for performing a process of bonding AlN whiskers 300 toinsulating particles 510. The container 3100 has a quasi-spheroidalshape. The container 3100 may have a spherical-like shape. The air pump3200 is provided tar circulating air in the container 3100 and forcausing AlN whiskers 300 to fly in the container 3100.

The particle inlet port 3300 is provided for introducing insulatingparticles 510 into the container 3100. Thus, the particle inlet port3300 is configured to be openable and closable. The heater 3400 isprovided for heating the interior of the container 3100. Thus, theheater 3400 can heat AlN whiskers 300 and insulating particles 510.

4. Production Method for Thermally Conductive Particulate

Firstly, an adhesive is applied to the surfaces of insulating particles510. Meanwhile, AlN whiskers 300 are placed in the production apparatus3000. In this case, the AlN whiskers 300 and the air in the container3100 may be heated by means of the heater 3400. The air in the container3100 is then circulated by means of the air pump 3200. The AlN whiskers300 fly with the circulating airflow. Subsequently, the adhesive-appliedinsulating particles 510 are supplied through the particle inlet port3300 into a region where the flying AlN whiskers 300 are present. Thus,the AlN whiskers 300 are bonded to the surfaces of the insulatingparticles 510 via the adhesive.

5. Production Method for Resin Molded Body

Numerous thermally conductive particulates TP1 are spread over a regionwhere the resin molded body 500 is to be formed. Thus, the thermallyconductive particulates TP1 are in contact with one another via the AlNwhiskers 300 on the surfaces of the particulates TP1. When thethus-spread thermally conductive particulates TP1 are solidified with aresin, a thermal conduction path is formed via the thermally conductiveparticulates TP1. Subsequently, a resin is introduced into gaps betweenthe thermally conductive particulates TP1. The resin may be any of thosedescribed in the fourth embodiment. The resin is then solidified, tothereby produce the resin molded body 500.

Sixth Embodiment

A sixth embodiment will now be described.

1. ZrO₂ Sensor (Sintered Body)

FIG. 16 schematically shows the structure of a ZrO₂ sensor A10 of thesixth embodiment. As shown in FIG. 16, the ZrO₂ sensor A10 is a sinteredbody containing AlN whiskers 100 and ZrO₂ particles 600. The ZrO₂particles 600 are insulating particles covering the AlN whiskers 100. Asdescribed below, the ZrO₂ sensor A10 contains Y₂O₃. Thus, Y₂O₃ ispresent in gaps between the ZrO₂ particles 600, gaps between the AlNwhiskers 100, and gaps between the ZrO₂ particles 600 and the AlNwhiskers 100.

The ZrO₂ particles 600 have a mean particle size of 1 μm to 100 μm.

2. AlN Whiskers

As shown in FIG. 1, the AlN whiskers 100 of the present embodiment arethe same as the AlN whiskers 100 of the first embodiment.

3. Production Method for AlN Whiskers

The production method for the AlN whiskers 100 of the present embodimentis the same as the production method for the AlN whiskers 100 of thefirst embodiment.

4. Production Method for ZrO₂ Sensor (Production Method for SinteredBody) 4-1. AlN Whisker Production Step

AlN whiskers 100 are produced as described above.

4-2. Mixture Preparation Step

A mixture of ZrO₂ particles 600 and Y₂O₃ particles is prepared.Specifically, ZrO₂ particles 600 (95 wt. %, to 98 wt. %) are mixed withY₂O₃ particles (2 wt. % to 5 wt. %) by means of, for example, a ballmill. The ZrO₂ particles 600 have a purity of 95% or more. The ZrO₂particles 600 have a mean particle size of 1 μm to 100 μm. The Y₂O₃particles have a purity of 95% or more. The particles have a meanparticle size of 1 μm to 100 μm.

4-3. AlN Whisker Mixing Step

AlN whiskers 100 (0.5 wt. % to 40 wt. %) are mixed with a mixture of theZrO₂ particles 600 and the Y₂O₃ particles (100 wt. %) by means of acommon mixing-stirring tool, such as a mixing-grinding machine or amortar. Thus, a mixture containing the AlN whiskers 100 is prepared.

4-4. Kneading Step

The mixture containing the AlN whiskers 100 (100 wt. %) is mixed withethyl alcohol (0.5 wt. % to 50 wt. %). The resultant mixture is formedinto a slurry by means of a stirrer. Thus, a slurry mixture is prepared.Water or another alcohol may be used instead of ethyl alcohol.

4-5. Molding Step

Subsequently, the slurry mixture is poured into a mold, to therebyprepare a first molded body.

4-6. Drying Step

The first molded body is then dried. The drying temperature is 60° C. to350° C. The drying time is one hour to three hours. These numericalranges are a mere example, and the drying temperature and time may fallwithin other ranges. Through this step, ethyl alcohol or water isevaporated from the first molded body. The atmosphere temperature of thefirst molded body may be increased at a rate of 1 to 10° C. per hour. Amicrowave oven may be used in this step.

4-7. Firing Step

Subsequently, the first molded body is fired by means of an evacuablefiring apparatus. The first molded body is placed in the firingapparatus, and then the firing apparatus is evacuated. Thereafter,nitrogen gas is supplied to the firing apparatus; i.e., the apparatus isin a nitrogen atmosphere. The internal atmosphere of the firingapparatus is then heated. For example, the atmosphere temperature isincreased from 350° C. to about 1,100° C. for about one hour. The Y₂O₃particles form a liquid phase in association with an increase in theatmosphere temperature. After the atmosphere temperature of the furnacehas reached 1,100° C., firing of the first molded body is initiated. Thefiring temperature is 1,100° C. to 1,600° C. The firing time is 10minutes to 10 hours. After the elapse of the firing time, the firingapparatus is cooled. For example, the firing apparatus may be cooled ata rate of 100° C. per hour. After the furnace temperature has beensufficiently lowered, the first molded body is removed therefrom.

4-8. Thermal Spraying Step

Subsequently, γ-Al₂O₃ is applied to the surface of the first molded bodyby means of thermal spraying. The γ-Al₂O₃ specific surface area is 300m² or more, preferably 1,000 m² or more. This step produces a secondmolded body including the first molded body and a γ-Al₂O₃ thermalspraying layer formed on the surface of the first molded body.

4-9. Catalyst Metal Deposition Step

Subsequently, the second molded body is immersed in an aqueous solutionor organic solution containing a catalyst metal. Examples of thecatalyst metal include Pt, Pd, Rd, and Rh. The second molded body isthen dried at a temperature of about 300° C. Thus, the ZrO₂ sensor A10is produced.

5. Effects of the Present Embodiment 5-1. Thermal Conductivity

The ZrO₂ sensor A10 of the present embodiment contain the AlN whiskers100 and the ZrO₂ particles 600. Since the ZrO₂ sensor A10 contains theAlN whiskers 100, it has a thermal conductivity higher than that of anyconventional sensor. Thus, the ZrO₂ sensor A10 of the present embodimenthas high-speed operability. The temperature distribution in the ZrO₂sensor A10 is more uniform. When the ZrO₂ sensor A10 is heated, the timerequired for increasing the internal temperature is shorter as comparedwith a conventional case. By virtue of these characteristic features,the ZrO₂ sensor A10 achieves high-accuracy oxygen measurement.

5-2. Mechanical Strength

The ZrO₂ sensor A10 of the present embodiment contains fibrous AlNwhiskers 100. The fibrous AlN whiskers 100 contribute to an increase inthe mechanical strength of the composite material. Thus, the ZrO₂ sensorA10 of the present embodiment has a mechanical strength higher than thatof any conventional ZrO₂ sensor.

Each AlN whisker 100 has on its surface an oxygen atom-containing layer120. Y₂O₃ forms a liquid phase during sintering. The liquid-phase Y₂O₃is readily bonded to oxygen atoms contained in the oxygenatom-containing layer 120 of the AlN whisker 100 or oxygen atomscontained in the ZrO₂ particles 600. Thus, the ZrO₂ sensor A10 has highmechanical strength.

5-3. Denseness

The AlN whiskers 100, the ZrO₂ particles 600, and Y₂O₃ are independentof one another in the ZrO₂ sensor A10, and these materials are stronglybonded together. Thus, virtually no gas enters the interfaces betweenthese materials.

6. Modifications 6-1. Insulating Particles

The ZrO₂ sensor A10 may contain insulating particles other than the ZrO₂particles 600. That is, the ZrO₂ sensor A10 contains one or more typesof insulating particles. For example, the ZrO₂ sensor A10 may contain.AlN polycrystalline particles. When the ZrO₂ sensor A10 contains AlNpolycrystalline particles in addition to the AlN whiskers 100, the ZrO₂sensor A10 exhibits improved thermal conductivity.

6-2. Sintering Aid

The ZrO₂ sensor A10 may contain an additional sintering aid in the formof insulating particles. For example, the ZrO₂ sensor A10 may contain,as sintering aids, CaO and LaB₆ in addition to Y₂O₃. Alternatively, theZrO₂ sensor A10 may contain, as sintering aids, CaO and B ₂O in additionto Y₂O₃. A sintered body can be produced even if such a sintering aid isused.

6-3. Atmosphere in Firing Apparatus

The ZrO₂ sensor A10 is produced through firing in a nitrogen atmosphere.In some cases, nitrogen gas may be mixed with a small amount of oxygengas. Thus, the atmosphere in the firing apparatus is anitrogen-containing atmosphere.

6-4. Al-Containing Material

The Al material used in the present embodiment is industrially refinedaluminum. However, an Al alloy may be used instead of such a high-purityAl material. AlN whiskers 100 can be produced even if such an Alatom-containing material is used. However, the use of industriallyrefined aluminum can reduce incorporation of impurities into theproduced AlN whiskers 100.

6-5. Oxygen Atom-Containing Layer

The oxygen atom-containing layer 120 contains at least one of Al₂O₃,AlON, and Al(OH)₃. However, the oxygen atom-containing layer 120 maycontain an oxygen atom-containing Al compound other than theaforementioned Al compounds. Thus, the oxygen atom-containing layer 120is a layer containing an Al atom and an oxygen atom.

6-6. Hot Pressing Step

A hot pressing step may be performed instead of the drying step andfiring step in the present embodiment. The hot pressing step ispreferably performed in a nitrogen atmosphere.

6-7. Combination

The aforementioned modifications may be combined in any manner.

7. Summary of the Present Embodiment

The ZrO₂ sensor A10 of the present embodiment contains the AlN whiskers100 and the ZrO₂ particles 600. Since the ZrO₂ sensor A10 contains theAlN whiskers 100, it has a thermal conductivity higher than that of anyconventional sensor. Thus, the ZrO₂ sensor A10 of the present embodimenthas high-speed operability.

Seventh Embodiment

A seventh embodiment will now be described.

1. Catalytic Converter (Sintered Body)

FIG. 17 is a perspective view of the external appearance of a catalyticconverter A20 of the seventh embodiment. The catalytic converter A20 isan automotive catalytic converter. As described below, the catalyticconverter A20 is a sintered body containing AlN whiskers 100 andcordierite. The catalytic converter A20 is a device for removing HC, CO,and NOx from engine exhaust gas. The catalytic converter A20 has asurface A21.

FIG. 18 is an enlarged view of the surface A21 of the catalyticconverter A20. As shown in FIG. 18, the surface A21 of the catalyticconverter A20 has numerous through holes A21 b. The through holes A21 bhave a quadrangular cross section. The through holes A21 b are definedby a wall A21 a. The through holes A21 b may have a hexagonal crosssection.

FIG. 19 is an enlarged view of the wall A21 a of the catalytic converterA20. The catalytic converter A20 Contains AlN whiskers 100 andcordierite 700. The AlN whiskers 100 are covered with the cordierite700. The cordierite 700 has a composition of 2MgO.2Al₂O₃.5SiO₂.

2. Production Method for Catalytic Converter (Production Method forSintered Body) 2-1. AlN Whisker Production Step

AlN whiskers 100 are produced as described in the first embodiment.

2-2. Mixture Preparation Step

A mixture of raw materials is prepared so as to achieve the compositionof the cordierite 700. For example, talc (3MgO.4SiO₂.H₂O), kaolin(Al₂O₃.2SiO₂.2H₂O), and alumina (Al₂O₃) are provided, and thesematerials are mixed in proportions so as to achieve the composition ofthe cordierite 700, to thereby prepare a mixture.

2-3. AlN Whisker Mixing Step

AlN whiskers 100 (0.5 wt. % to 40 wt. %) are mixed with theaforementioned mixture (mixture to achieve the composition of thecordierite 700) (100 wt. %) by means of a common mixing-stirring tool,such as a mixing-grinding machine or a mortar. Thus, a mixturecontaining the AlN whiskers 100 is prepared.

2-4. Kneading Step

The aforementioned mixture (mixture containing the AlN whiskers 100)(100 wt. %) is mixed with water (0.5 wt. % to 50 wt. %). The resultantmixture is formed into a slurry by means of a stirrer. Thus, a slurrymixture is prepared.

2-5. Molding Step

Subsequently, the slurry mixture is placed in a vacuum extruder. Theslurry mixture can be formed into, for example, a honeycomb,quadrangular, or triangular shape by means of this vacuum extruder. Afirst molded body is prepared through molding by means of the vacuumextruder.

2-6. Drying Step

The first molded body is then dried. The drying temperature is 15° C. to100° C. The drying time is one hour to three hours. These numericalranges are a mere example, and the drying temperature and time may fallwithin other ranges. Through this step, water is evaporated from thefirst molded body. A microwave oven may be used in this step.

2-7. Firing Step

Subsequently, the first molded body is fired by means of an evacuablefiring apparatus. The first molded body is placed in the firingapparatus, and then the firing apparatus is evacuated. Thereafter,nitrogen gas is supplied to the firing apparatus. In some cases,nitrogen gas may be mixed with a small amount of oxygen gas. Theinternal atmosphere of the firing apparatus is then heated. For example,the atmosphere temperature is increased from 20° C. to about 1,100° C.for about 24 hours. After the atmosphere temperature of the furnace hasreached 1,100° C. firing of the first molded body is initiated. Thefiring temperature is 1,100° C. to 1,500° C. The firing time is 24 hoursto 72 hours. After the elapse of the firing time, the firing apparatusis cooled. For example, the firing apparatus may be cooled at a rate of50° C. to 300° C. per hour. After the furnace temperature has beensufficiently lowered, the first molded body is removed therefrom.

2-8. Immersion Step

Subsequently, the first molded body is immersed in an aqueous γ-Al₂O₃solution. The γ-Al₂O₃ specific surface area is 300 m² or more,preferably 1,000 m² or more. Then, γ-Al₂O₃ is deposited on the surfaceof the first molded body, and the deposited γ-Al₂O₃ is dried, to therebyprepare a second molded body. Thereafter, the second molded body isdried at a temperature of 500° C. to 700° C.

2-9. Catalyst Metal Deposition Step

Subsequently, the second molded body is immersed in an aqueous solutionor organic solution containing a catalyst metal. Examples of thecatalyst metal include Pt, Pd, Rd, and Rh. The second molded body isthen dried at a temperature of about 300° C. Thus, the catalyticconverter A20 is produced.

3. Effects of the Present Embodiment 3-1. Thermal Conductivity

The catalytic converter A20 of the present embodiment contains the AlNwhiskers 100 and the cordierite 700. Since the catalytic converter A20contains the AlN whiskers 100, it has a thermal conductivity higher thanthat of any conventional catalytic converter. The temperaturedistribution in the catalytic converter A20 is more uniform.

3-2. Mechanical Strength

The catalytic converter A20 of the present embodiment contains fibrousAlN whiskers 100. Since the fibrous AlN whiskers 100 have toughness, thefibrous AlN whiskers 100 contribute to an increase in the mechanicalstrength of the composite material. Thus, the catalytic converter A20 ofthe present embodiment has a mechanical strength higher than that of anyconventional catalytic converter.

Therefore, the wall A21 a of the catalytic converter A20 can be designedto have a small thickness, and thus exhaust gas pressure loss can bereduced as compared with a conventional case.

4. Design of Catalytic Converter

The catalytic converter containing the AlN whiskers 100 has highmechanical strength. Thus, the catalytic converter of the presentembodiment can achieve a mesh of 1,000 cells/inch² to 3,000 cells/inch².The thickness of the wall A21 a can be adjusted to 100 μm to 200 μm. Anyconventional catalytic converter has a mesh of 600 cells/inch² to 1,000cells/inch² and a wall thickness of 200 μm to 500 μm.

5. Summary of the Present Embodiment

The catalytic converter A20 of present embodiment contains the AlNwhiskers 100 and the cordierite 700. Since the catalytic converter A20contains the AlN whiskers 100, it has a thermal conductivity higher thanthat of any conventional catalytic converter. Furthermore, the catalyticconverter A20 has a mechanical strength higher than that of anyconventional catalytic converter.

Eighth Embodiment

An eighth embodiment will now be described.

1. Automotive Windowpane (Sintered Body)

FIG. 20 is a perspective view of the external appearance of anautomotive windowpane A30 of the eighth embodiment. As described below,the automotive windowpane A30 is a sintered body containing AlN whiskers100 and glass.

FIG. 21 shows the internal structure of the automotive windowpane A30.The automotive windowpane A30 contains AlN whiskers 100 and glass 800.The AlN whiskers 100 are covered with the glass 800.

2. Production Method for Automotive Windowpane (Production Method forSintered Body) 2-1. AlN Whisker Production Step

AlN whiskers 100 are produced as described in the first embodiment.

2-2. Glass Particle Preparation Step

Firstly, class particles are prepared. For example, silica sand, sodaash, sodium sulfate (mirabilite), feldspar, limestone, and dolomite arefired in an oxygen atmosphere at about 1,600° C. The resultant firedproduct is pulverized into particles having a size of about 100 μm.

2-3. AlN Whisker Mixing Step

The pulverized particles (95 wt. %) are mixed with the whiskers 100 (5wt. %), to thereby prepare a mixture containing the AlN whiskers 100.The amount of the AlN whiskers 100 mixed may be a different value.

2-4. Molding Step

Subsequently, the mixture containing the AlN whiskers 100 is subjectedto molding, to thereby prepare a first molded body.

2-5. Firing Step

Subsequently, the first molded body is fired by means of an evacuablefiring apparatus. The first molded body is placed in the firingapparatus, and then the firing apparatus is evacuated. Thereafter,nitrogen gas is supplied to the firing apparatus. In some cases,nitrogen gas may be mixed with a small amount of oxygen gas. Theinternal atmosphere of the firing apparatus is then heated. For example,the atmosphere temperature is increased from 15° C. to about 1,100° C.for about 24 hours. After the atmosphere temperature of the furnace hasreached 1,000° C., firing of the first molded body is initiated. Thefiring temperature is 1,000° C. to 1,600° C. The firing time is one hourto 72 hours. After the elapse or the firing time, the firing apparatusis cooled. After the furnace temperature has been sufficiently lowered,the first molded body is removed therefrom. Thus, the automotivewindowpane A30 is produced.

3. Effects of the Present Embodiment 3-1. Thermal Conductivity

The automotive windowpane A30 of the present embodiment contains the AlNwhiskers 100 and the glass 800. Since the automotive windowpane A30contains the AlN whiskers 100, it has a thermal conductivity higher thanthat of any conventional automotive windowpane. The temperaturedistribution in the automotive windowpane A30 is more uniform.

3-2. Mechanical Strength

The automotive windowpane A30 of the present embodiment contains fibrousAlN whiskers 100. Since the fibrous AlN whiskers 100 have toughness, thefibrous AlN whiskers 100 contribute to an increase in the mechanicalstrength of the composite material. Thus, the automotive windowpane A30of the present embodiment has a mechanical strength higher than that ofany conventional automotive windowpane.

4. Modifications 4-1. Raw Materials of Glass Particles

The glass particles may be prepared from raw materials other than theaforementioned ones or any of combinations of the raw materials.

5. Summary of the Present Embodiment

The automotive windowpane A30 of the present embodiment contains the AlNwhiskers 100 and the glass 800. Since the automotive windowpane A30contains the AlN whiskers 100, it has a thermal conductivity higher thanthat of any conventional automotive windowpane. Furthermore, theautomotive windowpane A30 has a mechanical strength higher than that ofany conventional automotive windowpane.

Combination of Embodiments and Modifications Thereof

The first to eighth embodiments and modifications thereof may becombined in any manner.

EXAMPLES 1. Experiment 1 1-1. Experimental Procedure

A container 1210 accommodating an Al material is placed in a materialaccommodation unit 1200 of a production apparatus 1000. Subsequently,the interior of a furnace body 1100 is evacuated to about 500 Pa. Theinterior of the furnace body 1100 is then filled with argon gas.Thereafter, the material accommodation unit 1200 and a reaction chamber1300 are heated to 1,700° C., and nitrogen gas is introduced into thereaction chamber 1300. The processing time is about two hours.

1-2. Experimental Results

FIG. 22 is a photograph of AlN whiskers grown on an Al₂O₃ substrate. Asshown in FIG. 22, a large amount of AlN whiskers are grown on thesubstrate.

2. Experiment 2 2-1. Experimental Procedure

A container 1210 is placed in a material accommodation unit 1200 of aproduction apparatus 1000. AlN particles are accommodated in thecontainer 1210. The AlN particles have a size of about 0.2 μm to about10 mm. Subsequently, the interior of a furnace body 1100 is evacuated toabout 500 Pa. The interior of the furnace body 1100 is then filled withargon gas. Thereafter, the material accommodation unit 1200 and areaction chamber 1300 are heated to 1,700° C., and nitrogen gas isintroduced into the reaction chamber 1300. The processing time is abouttwo hours.

2-2. Experimental Results

FIG. 23 is a scanning micrograph of an AlN whisker (AlN whisker body)grown on AlN particles (part 1). As shown in FIG. 23, a fibrous smoothAlN whisker is grown on a portion of the surfaces of AlN particles.

FIG. 24 is a scanning micrograph of an AlN whisker (AlN whisker body)grown on AlN particles (part 2). As shown in FIG. 24, an AlN whiskerhaving irregularities is grown on a portion of the surfaces of AlNparticles. The irregularities correspond to a facet surface.

3. Experiment 3 3-1. Experimental Procedure

A container 1210 is placed in a material accommodation unit 1200 of aproduction apparatus 1000. Alumina particles are accommodated in thecontainer 1210. The alumina particles have a size of about 0.2 μm toabout 10 mm. Subsequently, the interior of a furnace body 1100 isevacuated to about 500 Pa. The interior of the furnace body 1100 is thenfilled with argon gas. Thereafter, the material accommodation unit 1200and a reaction chamber 1300 are heated to 1,700° C., and nitrogen gas isintroduced into the reaction chamber 1300. The processing time is abouttwo hours.

3-2. Experimental Results

FIG. 25 is a scanning micrograph of AlN whiskers (AlN whisker body)grown on alumina particles (part 1). As shown in FIG. 25, relativelystraight AlN whiskers are grown on the surfaces of alumina particles.

FIG. 26 is a scanning micrograph of an AlN whisker (AlN whisker body)grown on alumina particles (part 2). As shown in FIG. 26, a verystraight AlN whisker is grown on the surfaces of alumina particles.

4. Experiment 4 4-1. Experimental Procedure

Instead of an Al₂O₃ substrate 1310, a carbon substrate on which an AlNpolycrystalline film has been formed is placed in a production apparatus1000. AlN whiskers are grown on the AlN polycrystalline film in the samemanner as in Experiment 1.

FIG. 27 is a schematic cross-sectional view of the structure of a carbonsubstrate covered with AlN polycrystals. FIG. 28 is a schematiccross-sectional view of the structure of a carbon substrate covered withAlN particles.

4-2. Experimental Results

Also in this case, AlN whiskers are formed on the surfaces of the AlNpolycrystals.

5. Experiment 5 (Hydrophobization Treatment) 5-1. Experimental Method

Hydrophobization treatment was performed through the followingprocedure. Fibrous AlN single crystals (0.66 g) having an oxygenatom-containing layer were mixed with stearic acid (4.56 g), to therebyprepare a first mixture (AlN stearic acid=1:1 by mole). The firstmixture was mixed with cyclohexane (150 mL) to thereby prepare a secondmixture.

Subsequently, the second mixture was refluxed. The temperature of waterwas adjusted to 88.5° C. The reflux was performed for three hours. Afterthe elapse of three hours, the mixture was cooled to 40° C. and thensubjected to filtration, to thereby separate AlN whiskers from thesecond mixture. The AlN whiskers were washed with cyclohexane.Thereafter, the AlN whiskers were dried under reduced pressure for fiveminutes. Thus, the AlN whiskers 300 of the third embodiment wereproduced.

5-2. Experimental Results 5-2-1. Before Hydrophobization Treatment

FIG. 29 is a scanning micrograph of the AlN whiskers before thehydrophobization treatment. As shown in FIG. 29, the AlN whiskers have asmooth surface.

FIGS. 30 and 31 are oxygen mapping images of the AlN whiskers before thehydrophobization treatment as obtained by electron energy lossspectroscopy. FIG. 30 shows an oxygen atom-containing layer having athickness of 10 nm. FIG. 31 shows an oxygen atom-containing layer havinga thickness of 8 nm. Although these oxygen mapping images indicate thatthe oxygen atom-containing layer contains oxygen atoms, the compositionof the oxygen atom-containing layer is difficult to specify.

5-2-2. Comparison Between Before and After Hydrophobization Treatment

FIG. 32 is a scanning micrograph of the AlN whiskers before thehydrophobization treatment. FIG. 33 is a scanning micrograph of the AlNwhiskers after the hydrophobization treatment. These micrographsindicate that a thin layer was formed through the hydrophobizationtreatment. This thin layer corresponds to a hydrophobic layer 330. Sincethe hydrophobic layer 330 has a very small thickness, the AlN whiskersundergo almost no change in basic shape through the hydrophobizationtreatment. The AlN whiskers did not have staining caused by stearicacid. The presence of the hydrophobic layer 330 improves the adhesionbetween a resin material and the AlN whiskers 300.

6. Experiment 6 (Resin Molded Body Containing Aligned AlN Whiskers) 6-1.Experimental Method

AlN whiskers having a diameter of 1 μm to 3 μm and a length of 200 μm to500 μm were produced by the method of Experiment 1. The AlN whiskerswere aligned by means of the alignment apparatus 2000. While the firstends of the AlN whiskers were bonded to a tape, an epoxy resin was addedto the AlN whiskers. The mixing ratio of the AlN whiskers to the epoxyresin was 1 wt. %. While the AlN whiskers were aligned, the epoxy resinwas solidified under reduced pressure. This process produced a resinmolded body containing the AlN whiskers extending between the firstsurface and the second surface.

6-2. Experimental Results

The resin molded body was found to have a thermal conductivity of 3 W/mkto 5 W/mk between the first and second surfaces. The epoxy resin itselfwas found to have a thermal conductivity of about 0.2 W/mk. An increasein the amount of AlN whiskers to be added caused an increase in thethermal conductivity of the resin molded body. Thus, the method canproduce resin molded bodies having different thermal conductivities. AlNwhiskers (diameter: about 50 μm, length: about 10 mm) that had not beensubjected to hydrophobization treatment were found to have a thermalconductivity of about 250 W/mk.

7. Experiment 7 (AlN Whiskers) 7-1. Shape of AlN Whiskers

FIG. 34 is a scanning micrograph of the external appearance of AlNwhiskers 100. FIG. 35 is an enlarged scanning micrograph of an AlNwhisker 100. As shown in FIG. 35, a hexagonal single crystal is grown.

7-2. AlN Single Crystal

FIG. 36 is a transmission micrograph of an AlN whisker 100, As shown inFIG. 36, the AlN single crystal 110 is certainly in the form of singlecrystal.

7-3. Oxygen Atom-Containing Layer

FIG. 37 is an oxygen mapping image of an AlN whisker 100. In FIG. 37,white dots correspond to oxygen atoms. As shown in FIG. 37, an oxygenatom-containing layer having a thickness of 7 nm to 10 nm is present onthe surface of the AlN single crystal 110.

8. Experiment 8 (ZrO₂ Sensor) 8-1. Sample

There were prepared a ZrO₂ sensor containing AlN whiskers 100 (sampleA1: sensor of the sixth embodiment) and a ZrO₂ sensor containing no AlNwhiskers 100 (sample A2: conventional sensor). Sample A1 was found tocontain the AlN whiskers 100 in an amount of 1 wt. %.

8-2. Underwater Test

The two samples were heated and then placed in water. Thereafter, thepresence or absence of cracks was determined. Cracks were generated insample A1 when the sample was heated to about 450° C. to about 500° C.Meanwhile, cracks were generated in sample A2 when the sample was heatedto 400° C. Thus, sample A1 (i.e., sample of the sixth embodiment) hasthermal resistance higher than that of sample A2 (i.e., conventionalsample).

8-3. Heating Time

The two samples were heated to 600° C., and the time elapsed until theinterior of each sample reached 600° C. was measured. The elapsed timewas about 10 minutes in sample A1. The elapsed time was 20 minutes insample A2. Thus, sample A1 (i.e., sample of the sixth embodiment) has athermal conductivity sufficiently higher than that of sample A2 (i.e.,conventional sample).

8-4. Air-Fuel Ratio

The two samples were used to determine the air-fuel ratio of anautomotive engine. The air-fuel ratio in the case of sample A1 wascomparable to that in the case of sample A2.

9. Experiment 9 (Catalytic Converter) 9-1. Sample

There were prepared a catalytic converter containing AlN whiskers 100(sample B1: catalytic converter of the seventh embodiment) and acatalytic converter containing no AlN whiskers 100 (sample B2:conventional catalytic converter). Sample B1 was found to contain theAlN whiskers 100 in an amount of 5 wt. %.

9-2. Underwater Test

The two samples were heated and then placed in water. Thereafter, thepresence or absence of cracks was determined, Cracks were generated insample B1 when the sample was heated to about 700° C. Meanwhile, crackswere generated in sample B2 when the sample was heated to 600° C. Thus,sample B1 (i.e., sample of the seventh embodiment) has thermalresistance higher than that of sample B2 (i.e., conventional sample).Sample B1 (i.e., sample of the seventh embodiment) has mechanicalstrength higher than that of sample B2 (i.e., conventional sample).

9-3. Heating Time

The two samples were heated to 600° C., and the time elapsed until theinterior of each sample reached 600° C. was measured. The elapsed timewas about 10 minutes in sample B1. The elapsed time was 20 minutes insample B2. Thus, sample B1 (i.e., sample of the seventh embodiment) hasa thermal conductivity sufficiently higher than that of sample B2 (i.e.,conventional sample).

10. Brief Summary

AlN whiskers were able to be grown on various insulating substrates, AlNwhiskers are probably grown on a specific plane (e.g., (0001) plane) ofAlN particles or alumina particles. Thus, the crystal planes of AlNparticles or alumina particles correspond approximately to the crystalplanes of AlN whiskers. Conceivably, virtually no lattice defects arepresent between AlN particles or alumina particles and AlN whiskers.Therefore, the resultant AlN whisker body has high thermal conductivity.

A. Additional Remarks

According to a first aspect, there is provided a method for producingAlN whiskers, the method comprising heating an Al-containing material ina first chamber to thereby generate Al gas; and introducing the Al gasinto a second chamber through a first inlet port while introducingnitrogen gas into the second chamber through a second inlet port, tothereby grow AlN whiskers on the surface of an insulating substrateplaced in the second chamber.

In the method for producing AlN whiskers, the first chamber forgenerating Al gas is provided separately from the second chamber forgrowing AlN whiskers, and AlN whiskers are grown on the insulatingsubstrate in the second chamber. Thus, incorporation of other metalparticles into the grown AlN whiskers is prevented during recovery ofthe AlN whiskers.

In the method for producing AlN whiskers according to a second aspect,the insulating substrate is any of an Al₂O₃ substrate, an AlNpolycrystalline substrate, Al₂O₃ particles, and AlN particles. AlNwhiskers are readily grown on the surface of such an insulatingsubstrate.

In the method for producing AlN whiskers according to a third aspect,the atmosphere temperature in the second chamber is adjusted to 1,500°C. to 1,800° C. during growth of AlN whiskers. AlN whiskers areeffectively grown at such an atmosphere temperature.

According to a fourth aspect, there is provided an apparatus forproducing AlN whiskers, the apparatus comprising a materialaccommodation unit for accommodating an Al-containing material; areaction chamber for growing AlN whiskers; and a first heating unit forheating at least the material accommodation unit. The reaction chamberincludes one or more species of insulating substrates. The first heatingunit heats the Al-containing material accommodated in the materialaccommodation unit. The production apparatus has one or morecommunication portions that communicate between the materialaccommodation unit and the reaction chamber.

In the apparatus for producing AlN whiskers, the material accommodationunit for generating Al gas is provided separately from the reactionchamber for growing AlN whiskers, and AlN whiskers are grown on theinsulating substrate(s) in the reaction chamber. Thus, incorporation ofother metal particles into the grown AlN whiskers is prevented duringrecovery of the AlN whiskers.

In the apparatus for producing AlN whiskers according to a fifth aspect,the first heating unit heats the reaction chamber. Thus, the atmospheretemperature of the reaction chamber can be maintained at a temperaturesuitable for growth of AlN whiskers.

The apparatus for producing AlN whiskers according to a sixth aspectcomprises a second heating unit for heating the reaction chamber. Thus,the atmosphere temperatures of the material accommodation unit and thereaction chamber can be adjusted to different temperatures.

The apparatus for producing AlN whiskers according to a seventh aspectcomprises an openable and closable unit for switching the open state andthe closed state of an opening(s) of the one or more communicationportions. The openable and closable unit can control the timing ofintroduction of Al gas into the reaction chamber, and can also preventflow of nitrogen gas from the reaction chamber into the materialaccommodation unit.

In the apparatus for producing AlN whiskers according to an eighthaspect, the material accommodation unit is disposed vertically below thereaction chamber. Thus, Al gas generated in the material accommodationunit readily flows into the reaction chamber.

According to a ninth aspect, there is provided an AlN whisker bodycomprising an AlN particle or an Al₂O₃ particle, and an AlN whiskerbonded to the surface of the AlN particle or the Al₂O₃ particle. ThisAlN whisker body is a novel material.

According to a tenth aspect, there is provided an AlN whisker bodycomprising, a carbon substrate, an AlN polycrystal or AlN particleformed on the surface of the carbon substrate, and an AlN whisker bondedto the surface of the AlN polycrystal or the AlN particle.

According to an eleventh aspect, there is provided an AlN whiskercomprising a fibrous AlN single crystal, an oxygen atom-containing layercovering the AlN single crystal, and a hydrophobic layer covering theoxygen atom-containing layer. The oxygen atom-containing layer is formedthrough incorporation of at least oxygen atoms into the AlN singlecrystal. The hydrophobic layer has a hydrocarbon group.

The AlN whisker has high adhesion to a resin material, since thehydrophobic layer, which is formed through hydrophobization treatment,is readily bonded to the resin material. Thus, when the AlN whisker ismixed with a resin material to thereby produce a composite material,gaps are less likely to be generated between the AlN whisker and theresin material; i.e., the composite material has high thermalconductivity. The oxygen atom-containing layer is formed throughincorporation of at least oxygen atoms into the AlN single crystal.Thus, the crystallinity of the oxygen atom-containing layer is somewhatderived from the crystallinity of the AlN single crystal; i.e., theoxygen atom-containing layer has a dense crystalline structure.Therefore, oxygen atoms are less likely to reach deep into the oxygenatom-containing layer. Consequently, the oxygen atom-containing layerhas a thickness sufficiently smaller than that of an oxygenatom-containing layer formed through oxidation treatment of AlN. Theoxygen atom-containing layer formed through oxidation treatment of AlNhas a thickness of 1 μm or more.

In the AlN whisker according to a twelfth aspect, the oxygenatom-containing layer is bonded to the hydrophobic layer by means of anester bond.

In the AlN whisker according to a thirteenth aspect, the oxygenatom-containing layer contains at least one of Al₂O₃, AlON, and Al(OH)₃.

In the AlN whisker according to a fourteenth aspect, the oxygenatom-containing layer has a thickness of 7 nm to 500 nm.

According to a fifteenth aspect, there is provided a method forproducing AlN whiskers, the method comprising heating an Al-containingmaterial in a first chamber to thereby generate Al gas; introducing theAl gas into a second chamber through a first inlet port whileintroducing nitrogen gas into the second chamber through a second inletport; growing a fibrous AlN single crystal on the surface of aninsulating substrate placed in the second chamber; forming an oxygenatom-containing layer on the surface or the AlN single crystal; andforming a hydrocarbon group on the surface of the oxygen atom-containinglayer.

In the method for producing AlN whiskers according to a sixteenthaspect, the hydrocarbon group is formed by mixing the AlN single crystalhaving the oxygen atom-containing layer with stearic acid andcyclohexane, and refluxing the resultant mixture.

According to a seventeenth aspect, there is provided a resin molded bodycomprising an AlN whisker having a first end and a second end, and aresin material covering the AlN whisker. The resin molded body has afirst surface and a second surface opposite the first surface. The firstend of the AlN whisker is exposed at the first surface, and the secondend of the AlN whisker is exposed at the second surface.

In the resin molded body according to an eighteenth aspect, the anglebetween the axial direction of the AlN whisker and the first surface is60° to 120°.

In the resin molded body according to a nineteenth aspect, the AlNwhisker comprises a fibrous AlN single crystal, an oxygenatom-containing layer covering the AlN single crystal, and a hydrophobiclayer covering the oxygen atom-containing layer. The oxygenatom-containing layer is formed through incorporation of at least oxygenatoms into the AlN single crystal. The hydrophobic layer has ahydrocarbon group.

According to a twentieth aspect, there is provided a resin molded bodycomprising an insulating particle, a plurality of AlN whiskers coveringthe insulating particle, and a resin covering the AlN whiskers.

In the resin molded body according to a twenty-first aspect, the AlNwhisker comprises a fibrous AlN single crystal, an oxygenatom-containing layer covering the AlN single crystal, and a hydrophobiclayer covering the oxygen atom-containing layer. The oxygenatom-containing layer is formed through incorporation of at least oxygenatoms into the AlN single crystal. The hydrophobic layer has ahydrocarbon group.

According to a twenty-second aspect, there is provided a method forproducing a resin molded body, the method comprising applying anelectric field to an AlN whisker having a first end to thereby bond thefirst end of the AlN whisker to an adhesive member; impregnating the AlNwhisker, whose first end is bonded to the adhesive member, with a liquidresin; and solidifying the resin to thereby remove the adhesive memberfrom the first end of the AlN whisker.

According to a twenty-third aspect, there is provided a method forproducing a resin molded body, the method comprising applying anadhesive to the surfaces of insulating particles; causing AlN whiskersto fly by means of airflow; adding the adhesive-applied insulatingparticles to a region where the AlN whiskers fly, to thereby producethermally conductive particulates; and introducing a resin into gapsbetween the thermally conductive particulates.

According to a twenty-fourth aspect, there is provided sintered bodycomprising an AlN whisker including a fibrous AlN single crystal and anoxygen atom-containing layer covering the AlN single crystal, and one ormore species of insulating particles covering the AlN whisker. Theoxygen atom-containing layer is formed through incorporation of at leastoxygen atoms into the AlN single crystal.

Since the sintered body contains the AlN whisker, it has a thermalconductivity higher than that of any conventional sintered body. Thus,the temperature distribution in the sintered body is almost uniform.Since the AlN whisker has high toughness, the sintered body has amechanical strength higher than that of any conventional sintered body.The oxygen atom-containing layer is formed through incorporation of atleast oxygen atoms into the AlN single crystal. Thus, the crystallinityof the oxygen atom-containing layer is somewhat derived from thecrystallinity of the AlN single crystal; i.e., the oxygenatom-containing layer has a dense crystalline structure. Therefore,oxygen atoms are less likely to reach deep into the oxygenatom-containing layer. Consequently, the oxygen atom-containing layerhas a thickness sufficiently smaller than that of an oxygenatom-containing layer formed through oxidation treatment of AlN. Theoxygen atom-containing layer formed through oxidation treatment of AlNhas a thickness of 1 μm or more.

In the sintered body according to a twenty-fifth aspect, the oxygenatom-containing layer has a thickness of 7 nm to 500 nm.

In the sintered body according to a twenty-sixth aspect, the oxygenatom-containing layer contains at least one of Al₂O₃, AlON, and Al(OH)₃.

In the sintered body according to a twenty-seventh aspect, the one ormore species of insulating particles contain AlN polycrystallineparticles.

According to a twenty-eighth aspect, the sintered body is a ZrO₂ sensor,and the one or more species insulating particles contain ZrO₂.

According to a twenty-ninth aspect, the sintered body is a catalyticconverter, and the one or more species of insulating particles containcordierite.

According to a thirtieth aspect, the sintered body is an automotivewindowpane, and the one or more species of insulating particles containglass.

According to a thirty-first aspect, there is provided a method forproducing a sintered body, the method comprising heating anAl-containing material in a first chamber to thereby generate Al gas;introducing the Al gas into a second chamber through a first inlet portwhile introducing nitrogen gas into the second chamber through a secondinlet port; growing a fibrous AlN single crystal on the surface of aninsulating substrate placed in the second chamber; forming an oxygenatom-containing layer on the surface of the AlN single crystal; mixingthe AlN single crystal with one or more species of insulating particlesto thereby prepare a mixture; and firing the mixture to thereby producea sintered body.

In the method for producing a sintered body according to a thirty-secondaspect, the mixture is fired in a nitrogen-containing atmosphere.

In the method for producing a sintered body according to a thirty-thirdaspect, the sintered body is a ZrO₂ sensor, and the one or more speciesof insulating particles contain ZrO₂.

In the method for producing a sintered body according to a thirty-fourthaspect, the sintered body is a catalytic converter, and the one or morespecies of insulating particles contain cordierite.

In the method for producing a sintered body according to a thirty-fifthaspect, the sintered body is an automotive windowpane, and the one ormore species of insulating particles contain glass.

DESCRIPTION OF REFERENCE NUMERALS

-   100: AlN whisker-   110: AlN single crystal-   120: Oxygen atom-containing layer-   200: AlN whisker body-   210: AlN particle-   211: Surface-   300: AlN whisker-   300 a: First end-   300 b: Second end-   310: AlN single crystal-   320: Oxygen atom-containing layer-   330: Hydrophobic layer-   400: Resin molded body-   400 a: First surface-   400 b: Second surface-   410: Resin-   500: Resin molded body-   600: ZrO₂ particle-   700: Cordierite-   800: Glass-   1000: Production apparatus-   1100: Furnace body-   1200: Material accommodation unit-   1210: Container-   1220: Communication portion-   1220 a, 1220 b: Opening-   1230: Gas inlet port-   1300: Reaction chamber-   1310: Al₂O₃ substrate-   1320, 1330: Gas inlet port-   1340: Gas outlet port-   1400: Heater-   1500: Nitrogen gas supply unit-   1600: Argon gas supply unit-   A10: ZrO₂ sensor-   A20: Catalytic converter-   A30: Automotive windowpane

The invention claimed is:
 1. A method for producing AlN whiskers, themethod comprising: heating an Al-containing material in a first chamberto thereby generate Al gas; introducing the Al gas into a second chamberthrough a first inlet port while introducing nitrogen gas into thesecond chamber through a second inlet port; and growing AlN whiskers onthe surface of an insulating substrate placed in the second chamber. 2.A method for producing AlN whiskers according to claim 1, wherein theinsulating substrate is any of an Al₂O₃ substrate, an AlNpolycrystalline substrate, Al₂O₃ particles, and AlN particles.
 3. Amethod for producing AlN whiskers according to claim 1, wherein theatmosphere temperature in the second chamber is adjusted to 1,500° C. to1,800° C. during growth of AlN whiskers.
 4. A method for producing AlNwhiskers, the method comprising: heating an Al-containing material in afirst chamber to thereby generate Al gas; introducing the Al gas into asecond chamber through a first inlet port while introducing nitrogen gasinto the second chamber through a second inlet port; growing a fibrousAlN single crystal on the surface of an insulating substrate placed inthe second chamber; forming an oxygen atom-containing layer on thesurface of the AlN single crystal; and forming a hydrocarbon group onthe surface of the oxygen atom-containing layer.
 5. A method forproducing AlN whiskers according to claim 4, wherein, in formation ofthe hydrocarbon group, the method comprises mixing the AlN singlecrystal comprising the oxygen atom-containing layer with stearic acidand cyclohexane, and refluxing the resultant mixture.